> I'm still reading Michael's message but I don't see where he
> assumes we are pointing. Is it to zenith (airmass = 1.0)
> or down at the equator?
> Is atmospheric extinction built into the "photons from a mag
> zero star" constant?
Good point. The calculation assumes that one is looking at a
star _above_ the atmosphere, at an airmass of zero. The extinction
due to ordinary air is
20% in the V-band at zenith 30% in V-band at 45 degrees over
8% in the I-band 11% in I-band at 45 degrees over
So the numbers in my previous tables are slight overestimates of
the expected signal-to-noise.
--
-----
Michael Richmond "This is the heart that broke my finger."
mwrsps@rit.edu http://a188-L009.rit.edu/richmond/